Heat exchanger tubing by continuous extrusion

ABSTRACT

A heat exchanger tube having enhanced corrosion resistance and improved resistance to high burst pressures. The heat exchanger tube comprises an aluminum alloy that consists essentially of about 0.01-1.5% silicon, up to about 1.2% copper, up to about 2.0% manganese, about 0.01-1.0% iron, about 0.01-5.0% zinc, up to about 0.02% titanium and the balance substantially aluminum and incidental elements and impurities.

CROSS REFERNCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/633,076, filed on Dec. 3, 2004, the disclosure of which is fullyincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a single and multiple layer aluminumtube and a method for economically fabricating such a tube. Morespecifically, this invention discloses a method for manufacturingaluminum tube products with thin walls and fine features, such as micromulti void tubing, used in the manufacture of heat exchangers.

BACKGROUND OF THE INVENTION

Aluminum heat exchangers are used widely in the automotive industry.Applications include engine cooling systems where heat exchangers suchas radiators, oil coolers, charge air coolers and the like are employed.Additionally, passenger climate control systems also utilize heatexchangers as evaporators and condensers. Air conditioning systemstypically have two heat exchangers: condensers and evaporators.Condensers typically operate at elevated pressures (>500 psi) and mosttypically are made with extruded tubes. These tubes are produced viatraditional methods of extrusion. Most radiators use tubes made fromwelded or folded sheet (in part, due to the elevated costs per unitlength of extruded tubes versus tubes made from sheet and in part as aresult of the lower system pressure requirements of radiators (typically20 psi or less)). However, some radiator tubes are also manufactured byextrusion processes depending on the design and specific durabilityrequirements of the radiator in the field.

Typical extrusion based heat exchangers come essentially in two designs.The first design uses round tubing and bare (i.e. uncladed) fins thatare mechanically attached to the round tubes by first lacing the tubesinto holes punched in the fins, and then expanding the tubes to ensurethat the tube's outer surface is in close mechanical contact with thefins.

The second typical design uses flat tubing having a plurality ofchannels in the tubing, commonly referred to as multi void tubing ormicro multi void tubing. This type of heat exchanger tubing is attachedto the fins using a brazing process. The cross section of the flowchannels can vary, e.g., circular, oval, square, rectangular, of otherregular or irregular shapes. Typically, micro multi void and multi voidtubing are about 10-60 mm in width and about 1-2 mm in height.

Most aluminum extruded tubing products made for heat exchanger systemsare produced by using traditional billet extrusion methods, such aspress extrusion. As the alloy strength increases, the ability to usethese traditional methods of extrusion becomes less feasible due to thedifficulty of extruding the high strength alloy into a small tube. Thisdifficulty occurs because as the dimensions of the heat exchanger tubedecreases, the extrusion ratio, which is defined by a ratio of containerbore area and the total cross sectional area of extrusion, increasesthereby increasing the extrusion pressure needed to extrude the heatexchanger tube. The end result is that it is difficult (or sometimes notpossible) and at the least, very expensive to produce fine dimensionedtubing from high strength materials using traditional extrusion methods.This is becoming a barrier to the introduction of newer heat exchangerdesigns that utilize fine dimensioned tubing, particularly for nextgeneration designs where tubing must withstand very high pressures, forexample CO₂ refrigerant systems. In addition, as the heat exchangermanufacturers continue to work on next generation designs there is anincreasing need for thin walled tubing with finer features that has highstrength and high corrosion resistance, and in some instance highstrength at elevated service temperature. Therefore, heat exchangertubing might soon be required to operate at significantly higherpressures while at the same time becoming smaller in size as compared tocurrent heat exchanger designs with tubes that use R-134a as therefrigerant. In order to meet these increasing demands in a costeffective manner, it is critical that the heat exchanger tubes beextruded from higher strength alloys.

Therefore, there exists a need for an improved high strength heatexchanger tube that can withstand high burst pressures, exhibit goodcorrosion resistance, have small dimensions (e.g. 10 mm by 1 mm MMVtubing with micro void width less than 1 mm), and have fine internalfeatures. Additionally, there exists a need for a process toeconomically fabricate such a tube.

A continuous rotary extrusion process, known as the Conform™ Process,was developed and patented (U.S. Pat. No. 3,765,216) by the UnitedKingdom Atomic Energy Authority. In the Conform™ Process a rod orparticulate feedstock replaces the extrusion billet and thereby makingthe extrusion process continuous. The equipment used in the Conform™Process includes a grooved wheel, a coining roll, an abutment, a closefitting shoe, and an extrusion die. During the extrusion process thefeedstock is fed into a space formed by the grooved wheel, close fittingshoe, and abutment, and is heated and pressurized by the frictionbetween the rotating wheel and metal. When the metal temperature issufficiently high the pressure extrudes the metal through the extrusiondie.

For high volume aluminum tubing production requiring high productivity(lbs/hr), capital investment generally has not particularly favored theConform™ process (vs. the traditional billet extrusion process) becauseof developed multi-out capabilities of billet extruders (sometimes up to8 out) and differences in market pricing for feedstock rod vs. billet(i.e. billet is generally cheaper per pound for a specific alloy).Furthermore, it is a general perception in the industry that theConform™ process is more appropriate for simple, larger tolerance, lessdemanding shapes made from easy to extrude alloys like AA1060 forproducts such as spacer bars and the like. Hence the overwhelmingmajority of tubing is produced today via traditional billet basedextrusion processes.

However, the Conform™ process can make certain shapes with certainmetallurgical structures that billet based process cannot make due tothe process differences between the two processes, namely due to thedifferences in metallurgical structure of the rodstock and the reducedextrusion ratios (and resulting constancy of the die face pressure) ofthe Conform™ process.

Thus, there is a problem in the art, associated with the difficulty inextruding a small tube having a relatively complex structure, such as amicro multi void tubing, from a material with a high flow stress becausethe small tubing size increases the extrusion ratio, i.e. the crosssectional area ratio between the billet and the extruded product. Thisin turn increases the tonnage of pressure needed to extrude the alloyinto the desired shape and dimension, and effectively limits the alloychemistries that can be chosen as well as the allowable basemicrostructure of the metal being extruded to microstructures that havelow flow stresses. Hence billets are generally homogenized prior toextrusion, solute contents are generally low, and the billets aregenerally DC cast and preheated immediately prior to extrusion process.

SUMMARY OF THE INVENTION

The present invention is a response to the need for an improved heatexchanger tube, providing a method for producing an improved aluminum orheat exchanger tube at reduced costs and reduced manufacturing timeswhile utilizing higher strength alloys. The invention is furtherdirected to a heat exchanger tube having improved resistance to highburst pressures.

The heat exchanger tube is comprised of an aluminum alloy that consistsessentially of about 0.01-1.5% silicon, up to about 1.2% copper, up toabout 2.0% manganese, about 0.01-1.0% iron, up to about 5.0% zinc, up toabout 0.02% titanium, and the balance substantially aluminum andincidental elements and impurities. The aluminum alloy can furthercontain one or more of the following elements: about 0.01-0.35%chromium, about 0.01-0.35% zirconium, about 0.01-0.35% vanadium, about0.01-0.35% cobalt, up to about 1.0% magnesium, and about 0.01-2.5%nickel. The aluminum alloy is a feedstock that can be fabricated usingprocesses that are commonly known in the art.

In one embodiment, the feedstock can also be fabricated using acontinuously cast process. The feedstock could be a strip, rod, or sheethaving an aspect ratio ranging from about 1:1 to 500:1. The feedstockmay also be exposed to elevated temperatures greater than about 300° C.The feedstock has an average secondary dendrite arm spacing of less thanabout 100 microns, has a cross sectional area of about 2500 mm² or lessand has a yield strength ranging from about 50 to about 150 MPa. Thefeedstock is then extruded using a continuous rotary extrusion process.

After extrusion, the extrusion (e.g. heat exchanger tube) can bequenched using quenching processes that are commonly known in the art,such as still air cooling, force air cooling, spray water cooling,immersion in water, spray coolant cooling or immersion in coolant.

In one embodiment, the heat exchanger tube can further comprise a zinccoating of at least about 80 wt % zinc that is located on the exteriorsurface of the tube. The zinc coating can be applied to the exteriorsurface by coating processes that are commonly known in the art such asthermal spray, chemical vapor deposition, physical vapor deposition,cold spray or other metal deposition systems.

In one embodiment, the heat exchanger tube has a circumference less thanabout 400 mm.

In one embodiment, the heat exchanger tube is a micro multi void tubewith a maximum height not exceeding about 5 mm.

In one embodiment, one or more walls of the heat exchanger tube have awall thickness of less than about 1 mm.

In one embodiment, the heat exchanger tube has a post brazed tensileyield strength that exceeds about 35 MPa, preferably said tube has apost brazed tensile yield strength that exceeds about 45 MPa.

In one embodiment, the heat exchanger tube can withstand a burstpressure greater than about 69 bar. Similarly, the post braze heatexchanger tube can also withstand a burst pressure greater than about 69bar.

In one embodiment, the heat exchanger tube could have an electricconductivity that is above 48% IACS (International Annealed CopperStandard). The post braze heat exchanger tube could have an electricconductivity that is above 48% IACS.

In one embodiment, the invention is directed to a multi layered extrudedtube having improved resistance to high burst pressures. The multilayered tube has an inner core tube comprising an aluminum alloyconsisting essentially of about 0.01-1.5% silicon, up to about 1.2%copper, up to about 2.0% manganese, about 0.01-1.0% iron, up to about5.0% zinc, up to about 0.02% titanium, and the balance substantiallyaluminum and incidental elements and impurities, and one or more cladlayers comprising an aluminum alloy selected from the group consistingessentially of the 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, 7XXX, and 8XXXseries of aluminum alloys cladded on an exterior surface of said innercore. The inner core tube can further contain one or more of thefollowing elements: about 0.01-0.35% chromium, about 0.01-0.35%zirconium, about 0.01-0.35% vanadium, about 0.01-0.35% cobalt, up toabout 1.0% magnesium and about 0.01-2.5% nickel.

In one embodiment, the aluminum alloy used for the inner core is afeedstock that can be fabricated using processes that are commonly knownin the art. The feedstock can also be fabricated using a continuouslycast process. The feedstock could be a strip, rod, or sheet having anaspect ratio ranging from about 1:1 to 500:1. The feedstock may also beexposed to elevated temperatures greater than about 300° C. Thefeedstock has an average secondary dendrite arm spacing of less thanabout 100 microns, has a cross sectional area of about 2500 mm² or lessand has a yield strength ranging from about 50 to about 150 MPa. Thefeedstock is then extruded using a continuous rotary extrusion processinto an extrusion.

After extrusion, the extrusion (e.g. inner core tube) can be quenchedusing quenching process that are commonly known in the art such as stillair cooling, force air cooling, spray water cooling, immersion in water,spray coolant cooling or immersion in coolant.

One or more tangential continuous rotary extrusion machines is used toclad one or more clad layers onto the exterior surface of the inner coretube.

After cladding, one or more of the cladded layers can be drawn or sinkedover the inner core tube.

The multi layered extruded tube can further comprise a zinc coating ofat least about 80 wt % zinc that is located on the exterior surface ofthe tube. The zinc coating can be applied to the exterior surface bycoating processes that are commonly known in the art such as thermalspray, chemical vapor deposition, physical vapor deposition, cold sprayor other metal deposition systems.

One or more of the clad layers in the multi layered extruded tube can beselected from the Aluminum Association's 4343, 4045 and 4047 aluminumalloys, and have a thickness ranging from about 3 μm to about 300 μm.

One clad layer could have an electrochemical potential difference of atleast about 20 mV to about 40 mV (positive or negative) when compared tothe inner core tube or an adjacent clad layer as defined by the ASTM G69standard.

The multi layered extruded tube can be a micro multi void heat exchangertube having a circumference less than about 400 mm and a height notexceeding about 5 mm.

The feedstock is fabricated by using, but not limited to, continuouscasting followed by warm and cold work into rod, bar, plate, sheet, andother shapes that is used for the Conform™ Process. (While it ispossible to fabricate feedstock from DC (direct chill) based ingotprocess, it is generally more costly and the slower solidification ratesare generally less advantageous). The continuous casting process iscontrolled such that the metallurgical structure is obtained to meet thephysical, electrochemical, and mechanical property requirements for theextruded tube products. For instance, the composition and solidificationprocess can be controlled such that the alloy has high solute in solidsolution, fine particles for dispersoids strengthening, and balancedelectrochemical potentials between particles and matrix for excellentcorrosion resistance. The stock is thermally treated or non-thermallytreated according to the property requirements of the final product,which typically include mechanical properties, corrosion resistance,fatigue resistance, etc. For example, it is possible to form afterbraze, in the area where the extrusions come in contact with molten 4xxxbraze cladding, a dispersoid band of Al₁₂(Fe,Mn)₃Si particles in a low(<0.1%) Si 3003 type alloy after brazing, if the stock is nothomogenized prior to rotary extrusion. This post-brazed microstructurehas been shown to be highly corrosion resistance in splash typeenvironment in cars such as sheet based heat exchangers like radiators.

The continuous cast feedstock properties, such as dispersoid populationsor solute contents in solid solution, can be nearly retained in thefinal product due to a short thermal cycle in the Conform™ Process. Inthe billet extrusion process, the billets are almost always homogenizedand then heated up to extrusion temperature before extrusion. During thebillet homogenization, cooling after homogenization and extrusionpreheat processes some alloying elements in the billet precipitate. Thesolute precipitation changes the billet's metallurgical structure andthe resultant properties of final products. The Conform™ process itselfdoes not rely on a forced pre-heating step to elevate the material'stemperature (and hence lower the flow stress) to extrude the materialthrough the die(s). Immediately prior to Conform™ extrusion, the rodstock is fed into the wheel at room temperature and the materialundergoes tremendous shearing forces which rapidly elevates thetemperature of the material just prior to extrusion through the die. Theduration of this is very short vs. the pre-heat time employed in abillet extrusion process, hence giving the material little time toprecipitate solute. This advantage, when coupled with rod stock of theappropriate chemistry and processing history, can be used to producecertain products that have high strength through solute strengtheningand/or a fine dispersion of particles. In addition the electrochemicalproperties of final products can be appropriately tailored for theapplication by introducing some alloying elements into the stockmaterial at certain levels.

The Conform™ extrusion production process is continuous such that itgreatly minimizes transverse welds, reduces possible contamination oftenassociated with butt shearing and related pin hole leaks at billetchange compared to billet extrusion, and increases recoveries. Inaddition, the die face pressure remains consistent, which should resultin less tool wear, consistent die deflection, better dimensionaltolerances, and high quality. Moreover the one-feedstock andone-extruded product process (i.e. one out process) leads to possibleinline integration of other process such as flash anneal, coating, cutto length, etc.

The high strength aluminum alloys with yield strength greater than about50 MPa that may be used in this invention would include several of theAluminum Association's designated 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX,7XXX and 8XXX series of aluminum alloys. Other aluminum alloys that maybe used with this invention would include the alloys disclosed in U.S.Pat. Nos. 6,660,107; 6,656,296; 6,602,363; 6,503,446; 6,458,224; and5,976,278, the contents of which are incorporated herein by reference.

This invention may also be used to produce a clad tube product by useof, but no limited to, a tangential continuous rotary extrusion process.Depending upon the final application the clad tube can be formed withhigh strength aluminum alloy tube cladded with a layer of 1XXX, 2XXX,3XXX, 4XXX, 5XXX, 6XXX, 7XXX, or 8XXX series of aluminum alloy on theexterior surface of the tube. This cladding can be subjected to asinking or drawing and/or an elevated thermal process (e.g. an annealingoperation) to further enhance the adhesion of the cladding to the tube.

The invention also describes a method of making a heat exchanger tubethat includes continuously casting a feed stock and extruding the feedstock through a continuous extrusion rotary process to form a heatexchanger tube.

In one embodiment of this method, the heat exchanger tube is quenched orair cooled after extrusion.

An aspect of this invention is to provide improved heat exchanger tubingthat exhibits high strength, excellent corrosion resistance, andimproved mechanical properties as along with good formability,brazeability, fatigue performance and improved service life.

Another aspect of this invention is to produce micro multi void tubingexhibiting high strength, excellent corrosion resistance, and improvedmechanical properties as along with good formability, brazeability, andimproved service life.

Another aspect of this invention is to produce small dimension tubingthat exhibits high strength, excellent corrosion resistance, andimproved mechanical properties with good formability, fatigueresistance, brazeability, and improved service life.

Another aspect of this invention is to produce clad tube products withhigh strength aluminum alloy and a clad layer or layers for corrosionresistance improvement.

Another aspect of this invention is to produce clad tube products withan outer layer of braze filler alloy such that bare fin products can beused in the manufacture of heat exchangers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a multi void heat exchanger tube;

FIG. 2 is one embodiment of a continuous rotary extrusion apparatus; and

FIG. 3 is a flowchart depicting one embodiment of the present invention.

FIG. 4 is a three-layer round tube with clad on both inside and outsideof the tube.

FIG. 5 is a three-layer micro multi void tube with clad both inside andoutside tube.

FIG. 6 is an enhanced round tube with a clad layer on the outside tube.

FIGS. 7 a and 7 b are a micro multi void tube with a clad layer.

FIG. 8 is a four-layer micro multi void tube.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The accompanying drawings and the description which follows set forththis invention in its preferred embodiments. However, it is contemplatedthat persons generally familiar with extrusion processes will be able toapply the novel characteristics of the structures and methodsillustrated and described herein in other contexts by modification ofcertain details. Accordingly, the drawings and description are not to betaken as restrictive on the scope of this invention, but are to beunderstood as broad and general teachings. When referring to anynumerical range of values, such ranges are understood to include eachand every number and/or fraction between the stated range minimum andmaximum. For purposes of the description hereinafter, the terms “upper”,“lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the invention as it is oriented inthe drawing figures.

This invention solves the difficulty of extruding a high strength alloyinto a smaller, more complex structure by extruding a feedstock alloy ofcarefully selected chemistry and process history through a continuousrotary extrusion process. This extrusion process is known in the metalfabricating industry as the Conform™ Process, but applications of theprocess using high strength alloys to produce complex tubing structuresis unknown. The Conform™ Process is described in U.S. Pat. 3,765,216,the contents of which are incorporated herein by reference. This processincludes the steps of feeding metal, powder, or feedstock rod into oneend of a passageway formed between first and second members, with thesecond member having a greater surface area for engaging the materialthan the first member. The passageway is blocked at one end, remote fromthe feeding end, and has at least one die orifice associated with theblocked end. The moving of the passageway-defining surface of the secondmember relative to the passage-defining surface of the first member in adirection towards the die orifice from the first end to the blocked endis such that the frictional drag of the passageway-defining surface ofthe second member draws the material through the passageway andgenerates in it a pressure that is sufficient to extrude it through thedie orifice.

The advantage of using the Conform™ process to produce a smalldimensional tube is three fold. First, by using the Conform™ Process ahigh strength feedstock alloy can be used to produce the heat exchangertube. This advantage is possible because the feedstock in the Conform™Process is most typically, a continuous cast rod that is smaller indiameter than a billet. The smaller diameter of the continuous cast rodsignificantly reduces the extrusion ratio which in turn reduces thepressure necessary to extrude the desired product and the continuousnature of the process results in relatively constant die face pressure.Therefore, the Conform™ process allows a small size tube to be extrudedusing a high strength alloy. The second advantage that the Conform™process presents is that it is cost competitive for certain difficult toextrude profiles and has the advantage of being a continuous process.The continuous process generally has high productivity and highrecoveries (typically 5% process scrap or less) which in turn helps tokeep the production costs competitive. Finally, by using the continuousrotary extrusion process, a non-homogenized or homogenized castfeedstock of high solute level may be used to extrude a tube that hasimproved strength properties and/or corrosion properties, which offersalloy design flexibility in chemistry and processing history of alloy.

It is a great advantage to achieve improved strength properties of theextruded tube by exploiting higher solute alloys, particularlycontinuous cast high solute alloys and having the metallurgicalflexibility of using homogenized or non homogenized feedstock rod.Extruding a micro multi void tube using a non-homogenized cast billetthrough traditional press extrusion methods would be extremely difficultdue to the high extrusion pressure that would be needed to extrude thedesired product. Unlike extruding a product with a press extrusionmethod, the Conform™ Process requires a lower extrusion pressure sincethe Conform™ Process has a lower extrusion ratio. Because the Conform™Process requires lower extrusion pressure, it is possible to extrude asmall dimensional tube from a high flow stress material (e.g. anon-homogenized cast rod or high solute level alloy). By using thecontinuous rotary extrusion process in combination with high strengthaluminum alloys and microstructures, this invention allows heatexchanger tubing to be produced with a high strength alloy while beingefficient and cost competitive from a manufacturing perspective. TABLE 1Metallurgical Composition of the Aluminum Alloys Si Cu Mn Fe Zn Ti Cr ZrV Co Mg Ni about up to up to about up to up to Balance — — — — — —0.01-1.5% about about 0.01-1.0% about about substantially 1.2% 2.0% 5.0%0.02% aluminum and incidental elements and impurities about up to up toabout up to up to Balance about about about about up to about 0.01-1.5%about about 0.01-1.0% about about substantially 0.01-0.35% 0.01-0.35%0.01-0.35% 0.01- about 0.01-2.5% 1.2% 2.0% 5.0% 0.02% aluminum 0.35%1.0% and incidental elements and impurities about up to up to about upto about Balance — — — — — — 0.01-1.5% about about 0.01-1.0% about0.02-0.35% substantially 1.2% 2.0% 5.0% aluminum and incidental elementsand impurities about up to upto about up to about Balance about aboutabout about up to about 0.01-1.5% about about 0.01-1.0% about 0.02-0.35%substantially 0.01-0.35% 0.01-0.35% 0.01-0.35% 0.01- about 0.01-2.5%1.2% 2.0% 5.0% aluminum 0.35% 1.0% and elements and impurities about upto up to about up to up to Balance — — — — — — 0.01-1.0% about about0.05-0.8% about about substantially 1.0% 1.8% 2.0% 0.02% aluminum andincidental elements and impurities about up to up to about up to up toBalance about about about about up to about 0.01-1.0% about about0.05-0.8% about about substantially 0.01-0.30% 0.01-0.30% 0.01-0.30%0.01- about 0.01-2.0% 1.0% 1.8% 2.0% 0.02% aluminum 0.30% 0.08% andincidental elements and impurities about up to up to about up to aboutBalance — — — — — — 0.01-1.0% about about 0.05-0.8% about 0.02-0.30%substantially 1.0% 1.8% 2.0% aluminum and incidental elements andimpurities about up to up to about up to about Balance about about aboutabout up to about 0.01-1.0% about about 0.05-0.8% about 0.02-0.30%substantially 0.01-0.30% 0.01-0.30% 0.01-0.30% 0.01- about 0.01-2.0%1.0% 1.8% 2.0% aluminum 0.30% 0.08% incidental elements and impuritiesabout up to up to about up to up to Balance — — — — — — 0.01-0.50% aboutabout 0.10-0.7% about about substantially 0.7% 1.5% 1.5% 0.02% aluminumand incidental elements and impurities about up to up to about up to upto Balance about about about about up to about 0.01-0.50% about about0.10-0.7% about about substantially 0.01-0.28% 0.01-0.28% 0.01-0.28%0.01- about 0.01-1.8% 0.7% 1.5% 1.5% 0.02% aluminum 0.28% 0.08% andincidental elements and impurities about up to up to about up to aboutBalance — — — — — — 0.01-0.50% about about 0.10-0.7% about 0.02-0.25%substantially 0.7% 1.5% 1.5% aluminum and incidental elements andimpurities about up to up to about up to about Balance about about aboutabout up to about 0.01-0.50% about about 0.10-0.7% about 0.02-0.25%substantially 0.01-0.28% 0.01-0.28% 0.01-0.28% 0.01- about 0.01-1.8%0.7% 1.5% 1.5% aluminum 0.28% 0.08% and incidental elements andimpurities

Table 1 discloses the metallurgical compositions of the aluminum alloysthat can be used to fabricate a heat exchanger tube in accordance withthis invention. One skilled in the art would also appreciate that theheat exchanger tube can have one or more clad layers cladded over anexterior surface of the tube. The clad layer can be selected from theAluminum Association's 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, 7XXX, or 8XXXseries of aluminum alloys.

FIG. 1 is a cross section of a multi void heat exchanger tube. FIG. 1depicts a multi void tube 2 having a plurality of parallel flow channels4 that are separated by a web(s) or wall(s) 6 that are aligned along thelongitude of the tubing or generally perpendicular to the opposingsurfaces 8 and 10. As can be seen in FIG. 1, the flow channels 4 aresubstantially rectangular. However, one skilled in the art wouldappreciate that the cross section of the flow channels 4 can have othershapes (e.g., square, circular, oval, or other regular or irregularshapes). The inner walls of the channels 4 can be smooth or rough. Inmaking a heat exchanger, the tubes 2 are joined to corrugated fins (notshown) using a brazing process. Both multi void and micro multi voidtubing 2 are about 10-25 mm in width and about 1-2 mm in height.

A high strength heat exchanger tube will soon be required as theindustry adopts carbon dioxide as the standard coolant for heatexchanger systems since carbon dioxide heat exchangers operate at higherpressures than heat exchangers that utilize Freon. By using continuouscasting and the Conform™ Process a heat exchanger tube can be producedwith both high strength and improved corrosion resistant and servicelife, which will be in great favor of future automotive heat exchangerapplications. A heat exchanger tube formed from a high strength andcorrosion resistant aluminum alloy would not only meet the increasingdemands for the new generation heat exchangers, but provide betterservice life and durability as well for automotives encountering saltand snow during the winter months, automobiles located in or near costalareas with high sodium chloride levels in the air, and potentialcorrosion from other elements or materials that might be mixed with rainwater.

FIG. 2 is one example of a continuous rotary extrusion apparatus, alsoknown as the Conform™ Process. The extrusion apparatus comprises a wheel1 rotate-ably mounted on a shaft 2. The wheel 1 has a groove 3 machinedaround its outer edge about the axis of the wheel. A shoe member 4 fitsclosely against the edge of the wheel 1. An abutment member 5 formed onthe underside of the shoe member 4 projects into the groove 3 and iscomplementary in shape to the groove cross section so as to block thegroove with a sliding fit. The abutment member 5 has an extrusionorifice 6. A chamber 7 integrally formed with the shoe member 4 has abore 8 connected with the groove 3 in the wheel 1. A sealing block 9formed on the underside of the shoe member 4 at the opposite end to theabutment member 5 projects into and is close sliding fit in thecircumferential groove 3 in the wheel 1.

The wheel 1 is rotated clockwise as shown by the arrow 11 in FIG. 2. Thematerial 10 in the grove 3 beneath the shoe member 4 is carried forwardtowards the abutment member 5 by the frictional drag of the walls of thegroove 3. Thus pressure is generated in the material in the groove 3, sothat the material is extruded through the orifice 6 in the abutmentmember 5. Also the rotation of the wheel 1 drags material under atransverse shearing action from the bore 8 of the chamber 7 so that acontinuous extrusion of the material is obtained.

FIG. 3 is a flowchart depicting one preferred embodiment of theinventive method. As can be understood from FIG. 3, the continuouslycast feedstock rod is formed by cooling molten metal into a bar shape,which is continuously formed into a rod by a number of rollers followinginitial cooling. The feedstock rod is then fed into a groove located ona rotating wheel and extruded through the extrusion die to form themicro multi void tubes. After extrusion, the micro multi void tubes canthen be quenched using techniques that are commonly known in the artsuch as water or air cooling.

FIG. 4 shows an example of a multi layer round tube 2. The multi layertube 2 has an inner core tube 4, an intermediate layer 6, and an outerlayer 8. In one application, the inner core tube 4 and the outer layer 8are anodic (at least 20 mV more negative) to intermediate layer 6 suchthat the two layers enhance the corrosion resistance of the tube.However, the intermediate layer 6 can be a high strength alloy. Inanother application the outer layer 8 is made of a 4XXX aluminum alloycladding for braze, the inner core tube 4 has a high magnesium content(up to 2%) for high strength, and the intermediate layer 6 has a lowmagnesium (up to 0.15%) content, ideally less than 0.05%, to enhance thebrazeability.

FIG. 5 depicts a multi layer micro multi void tube 2. The multi layermicro multi void tube 2 has an inner core tube 4, an intermediate layer6, and an outer layer 8. In one application the inner core tube 4 andthe outer layer 8 are anodic (at least 20 mV more negative) tointermediate layer 6 such that the two layers enhance the corrosionresistance of the tube. However, the intermediate layer 6 can be a highstrength alloy. In another application the outer layer 8 is made of a4XXX series aluminum alloy cladding for braze, the inner core tube 4 hasa high magnesium content (up to 2%) for high strength, and theintermediate layer 6 has a low magnesium (up to 0.15%) content, ideallyless than 0.05%, to enhance the brazeability.

FIG. 6 depicts a round tube 2 with an inner core 4 and an outer layer 6.The outer layer 6 is used for applications such braze or corrosionimprovement. However, it is noted that one skilled in the art wouldrecognize that the outer layer might be used for other applications aswell yet still fall within the scope of this invention. The inner core 4can be fabricated from a high strength alloy which can withstand highburst pressures and which exhibits enhance heat transfer properties.

FIGS. 7 a and 7 b show a two layer micro multi void tube 2 having aninner core 4 and an outer layer 6. The inner core has a first end 8, asecond end 10, an upper surface 12, and a lower surface 14. As depictedin FIG. 7 a, the outer layer 6 can be made to cover only the uppersurface 12 and the lower surface 14 of the inner core 4 while excludingthe first end 8 and the second end 10. FIG. 7 b depicts the outer layer6 as covering the entire inner core 4 including the first and secondends 8 and 10.

FIG. 8 is an example of four layer micro multi void tube 2 having aninner core 4, a first intermediate layer 6, a second intermediate layer8, and an outer layer 10. Each of the layers are designed for a specificproperty requirement. For example, some properties that might be desirewould include, but shall not be limited to, high strength, highcorrosion resistance, solute diffusion control, and improvedbrazeability. TABLE 2 Pre and Post Braze Tensile Properties of MMVTubing Pre Braze Post Braze Tubing Tensile Yield Elong Tensile YieldElong Alloy Feedstock Homogenization Design (MPa) (MPa) (%) (MPa) (MPa)(%) 1350 Concast No MMV 66.21 37.13 50.3 57.93 16.21 35.3 High ConcastNo MMV 97.47 69.43 40.3 91.72 34.02 47.7 Strength (A) Alloy HighExtruded Yes MMV 91.72 51.95 43.1 90.00 30.23 37.4 Strength from a AlloyDC Cast Billet (B)

In Table 2, the high strength alloys are the same aluminum alloy andwere selected from the 3XXX series of aluminum alloys. The high strengthaluminum alloy consisted essentially of about 0.01-1.0% silicon, up toabout 0.70% copper, up to about 2.0% manganese; about 0.01-1.0% iron,about 0.01-5.0% zinc; about 0.01-0.35% titanium, balance substantiallyaluminum and incidental elements and impurities. Aluminum alloy 1350 wasused as a control material.

High Strength Alloy Concast (A) and the 1350 aluminum alloy were formedinto feedstock rods by a continuous casting process. The feedstock rodswere then extruded into various micro multi void tubes (MMV) through theConform™ Process. In contrast, High Strength Alloy DC Cast Billet (B)was extruded into a feedstock rod by using a traditional press extrusionmethod with a DC cast billet. The extruded feedstock rod was thenextruded into MMV tubes through the Conform™ Process. The Conform™Process had an extrusion ratio of 4 as compared to traditional pressextrusion which as an extrusion ratio 450. Table 2 shows that when thehigh strength aluminum alloy is extruded through the Conform Processwith a feedstock rod that was continuously cast and not homogenized, theextruded tube exhibited equal or higher pre and post brazed strengthproperties when compared to DC Cast Billet (B).

The results in Table 2 were unexpected results since one would notexpect that a non-homogenized high strength alloy could be extruded to asmall size MMV tube meeting all the dimensional and surface qualityrequirements. In addition, Table 2 shows that when the feedstock rod wasformed by continuous casting (Concast (A)), the extruded MMV tubeexhibited improved tensile properties over an MMV tube that was formedfrom a feedstock rod that was extruded from a DC cast billet usingtraditional press extrusion methods (DC Cast Billet (B)). For example,Table 2 shows that the Pre-braze tensile strength of the MMV tube thatwas formed by continuous casting (Concast (A)) had a tensile strength of97.47 MPa, which is a 6% increase in tensile strength when compared tothe MMV that was extruded DC Cast Billet (B), and a yield strength of69.43 MPa, which is a 25% increase in yield strength when compared tothe MMV that was extruded using DC Cast Billet (B). Table 2 also showsthat the pre braze MMV had a 40.3% elongation. The post braze MMV thatwas formed by continuous casting (Concast (A)) had a tensile strength of91.72 MPa, which is a 2% increase in tensile strength when compared tothe MMV that was extruded using DC Cast Billet (B), a yield strength of34.02 MPa, which is an 11% increase in yield strength when compared tothe MMV that was extruded using DC Cast Billet (B), and an elongation of47.7%, which is a 22% increase in elongation when compared to the MMVthat was extruded using DC Cast Billet (B). Therefore, a heat exchangertube exhibiting improved tensile properties can be manufactured by usingthe Conform™ Process in combination with feedstock rod formed bycontinuous casting.

Since High Strength Alloy Concast (A) exhibited improved tensileproperties over High Strength Alloy DC Cast Billet (B), Table 2 is anindication (for dispersion strengthened or age hardened or solutestrengthened alloys) that the tensile properties of heat exchangertubing (of like chemistry) that is extruded through a combination ofcontinuous casting and the Conform™ Process would be greater than thetensile properties of tubing that is extruded using a billet andtraditional press extrusion methods. This conclusion can be assertedbecause the microstructure of the extruded feedstock rod wassubstantially similar to that of the original billet and both theConform™ Process and the traditional press extrusion is believed to havesubstantially similar metal temperatures and metal flow at the momentthe metal is being extruded through the extrusion die. Therefore, it isreasonable to conclude that heat exchanger tubes extruded using theConform™ Process would exhibit improved tensile properties over heatexchanger tubes that are extruded using a billet and traditional pressextrusion methods. TABLE 3 Corrosion Test (SWAAT) Results (number passedover total number tested) Rod Design Alloy Stock Code 10 Days 20 Days 30Days 1350 Concast MMV 14/15  6/15  0/15 High Strength Concast MMV 15/1515/15 15/15 Alloy (A) High Strength Extruded MMV 15/15 15/15 15/15 Alloyfrom a DC Cast Billet (B) High Strength Billet Production — 5/5 5/5Alloy (C)

Table 3 shows the number of extruded tubes that passed the SWAAT test inthe braze condition. The SWAAT test used was the American Society forTesting and Materials (ASTM) G85 A3. The high strength alloy wasselected from the 3XXX series of aluminum alloys. The high strengthaluminum alloy consisted essentially of about 0.01-1.0% silicon, up toabout 0.70% copper, up to about 2.0% manganese; about 0.01-1.0% iron,about 0.01-5.0% zinc; about 0.01-0.35% titanium, balance substantiallyaluminum and incidental elements and impurities. Aluminum alloy 1350 wasused as a control material and the feedstock rod was extruded using acontinuous casting process.

High strength alloy continuous cast (Concast) (A), high strength alloydirect chill (DC) cast billet (B), and aluminum alloy 1350 were extrudedinto heat exchanger tubing using the Conform™ Process. High strengthalloy billet (C) was extruded into heat exchanger tubing by usingtraditional press extrusion methods. Table 3 shows that the tubesextruded by the Conform™ Process with the high strength aluminum alloyexhibited similar corrosion resistance properties as compared to thetubes that were extruded with a billet by traditional press extrusionmethods. As expected, the corrosion resistance of the high strengthalloy was superior to that of the control 1350 aluminum alloy. Table 3shows that the Conform™ Process can be used to produce a heat exchangertube with identical anti-corrosive properties as that of a tube that isproduced using traditional press extrusion methods. TABLE 4 SurfaceRoughness Test Results of Experimental MMV Tubing Alloy-Sample RodDesign R_(a) R_(q) R_(p) R_(v) R_(t) R_(z) R_(max) ID Stock Code (μm)(μm) (μm) (μm) (μm) (μm) (μm) 1350-B23B Concast MMV Pass Pass Pass PassPass Pass Pass High Strength Concast MMV Pass Pass Pass Pass Pass PassPass Alloy (A) High Strength Extrude MMV Pass Pass Pass Pass Pass PassPass Alloy from a DC Cast Billet (B) Commercially 10 10 10 10 10 10 10Acceptable Standards

Table 4 shows the pre braze surface roughness measurements of the tubesthat were extruded using the Conform™ Process. As with the previoustrials, the high strength alloy was selected from the 3XXX series ofaluminum alloys. Aluminum alloy 1350 was used as a control material. Allof the alloys were extruded into a micro multi void (MMV) tube. Themeasurements were taken normal to the extrusion direction and themeasurements include the following: R_(a)—roughness average, R_(q)—rootmean squared roughness average, R_(p)—maximum peak height, R_(v)—maximumvalley depth, R_(t)—maximum roughness depth, R_(z)—mean peak-to-valleyheight, and R_(max)—Maximum peak-to-valley height.

Table 4 shows that the tubes that were extruded using the Conform™Process exceed the current commercially acceptable standards in therelevant industry. This result was the same regardless if the feedstockrod was formed by continuous casting or by extrusion by a DC castbillet. Therefore, a heat exchanger tube with small dimensions andimproved tensile properties can be produced using the Conform™ Processwith surface roughness equivalent to that of tubes extruded usingtraditional press extrusion methods.

Having described the presently preferred embodiments, it is to beunderstood that the invention may be otherwise embodied within the scopeof the appended claims.

1. A heat exchanger tube having improved resistance to high burstpressures, said heat exchanger tube comprising an aluminum alloy thatconsists essentially of about 0.01-1.5% silicon, up to about 1.2%copper, up to about 2.0% manganese, about 0.01-1.0% iron, up to about5.0% zinc, up to about 0.02% titanium, and the balance substantiallyaluminum and incidental elements and impurities, wherein said heatexchanger tube is formed from an aluminum alloy feedstock, saidfeedstock being a strip, rod, or sheet having an aspect ratio rangingfrom about 1:1 to 500:1, said feedstock may be exposed to elevatedtemperatures greater than about 300° C., said feedstock having anaverage secondary dendrite arm spacing less than about 100 microns andhaving a cross sectional area of about 2500 mm² or less and having ayield strength ranging from about 50 to about 150 MPa, and wherein saidfeedstock is extruded using a continuous rotary extrusion process intoan extrusion.
 2. An improved heat exchanger tube according to claim 1wherein said extrusion is quenched or air cooled after extrusion.
 3. Animproved heat exchanger tube according to claim 1 wherein said aluminumalloy feedstock is continuously cast.
 4. An improved heat exchanger tubeaccording to claim 1 wherein said aluminum alloy further contains one ormore of the following elements: about 0.01-0.35% chromium, about0.01-0.35% zirconium, about 0.01-0.35% vanadium, about 0.01-0.35%cobalt, up to about 1.0% magnesium, and about 0.01-2.5% nickel.
 5. Animproved heat exchanger tube according to claim 1 wherein said tubefurther comprises a coating of at least about 80 wt % zinc.
 6. Animproved heat exchanger tube according to claim 1 wherein said tube hascircumference less than about 400 mm.
 7. An improved heat exchanger tubeaccording to claim 1 wherein said tube is a micro multi void tube with amaximum height not exceeding about 5 mm.
 8. An improved heat exchangertube according to claim 1 wherein one or more walls of said tube has awall thickness of less than about 1 mm.
 9. An improved heat exchangertube according to claim 1 wherein said tube has a post brazed tensileyield strength that exceeds about 35 MPa.
 10. An improved heat exchangertube according to claim 1 wherein said tube has a post brazed tensileyield strength that exceeds about 45 MPa.
 11. An improved heat exchangertube according to claim 1 wherein said tube can withstand a burstpressure greater than about 69 bar.
 12. An improved heat exchanger tubeaccording to claim 1 wherein said tube can withstand a burst pressuregreater than about 69 bar post braze.
 13. An improved heat exchangertube according to claim 1 wherein said tube has an electric conductivitythat is above about 48% IACS.
 14. An improved heat exchanger tubeaccording to claim 1 wherein said tube has a post-braze electricconductivity that is above about 48% IACS.
 15. A heat exchanger tubehaving enhanced corrosion resistance and improved resistance to highburst pressures, said heat exchanger tube comprising an aluminum alloythat consists essentially of about 0.01-1.5% silicon, up to about 1.2%copper, up to about 2.0% manganese, about 0.01-1.0% iron, up to about5.0% zinc, about 0.02-0.35% titanium, and the balance substantiallyaluminum and incidental elements and impurities, wherein said aluminumalloy is continuously cast into a feedstock, said feedstock being astrip, rod, or sheet and having an aspect ratio ranging from about 1:1to 500:1, said feedstock may be exposed to elevated temperatures greaterthan about 300° C., said feedstock having an average secondary dendritearm spacing less than about 100 microns and having a cross sectionalarea of about 2500 mm² or less and having a yield strength ranging fromabout 50 to about 150 MPa, and wherein said feedstock is extruded usinga continuous rotary extrusion process into an extrusion, and quenchingsaid extrusion.
 16. An improved heat exchanger tube according to claim15 wherein said aluminum alloy further contains one or more of thefollowing elements: about 0.01-0.35% chromium, about 0.01-0.35%zirconium, about 0.01-0.35% vanadium, about 0.01-0.35% cobalt, up toabout 1.0% magnesium, and about 0.01-2.5% nickel.
 17. An improved heatexchanger tube according to claim 15 wherein said tube further comprisesa coating of at least about 80 wt % zinc.
 18. A heat exchanger tubehaving enhanced corrosion resistance and improved resistance to highburst pressures, said heat exchanger tube comprising an aluminum alloythat consists essentially of about 0.01-1.0% silicon, up to about 1.0%copper, up to about 1.8% manganese, about 0.05-0.8% iron, up to about2.0% zinc, up to about 0.02% titanium, and the balance substantiallyaluminum and incidental elements and impurities, wherein said aluminumalloy is continuously cast to fabricate a feedstock, said feedstockbeing a strip, rod, or sheet and having an aspect ratio ranging fromabout 1:1 to 500:1, said feedstock may be exposed to elevatedtemperatures greater than about 300° C., said feedstock having anaverage secondary dendrite arm spacing less than about 100 microns andhaving a cross sectional area of about 2500 mm² or less and having ayield strength ranging from about 50 to about 150 MPa, and wherein saidfeedstock is extruded using a continuous rotary extrusion process intoan extrusion, and quenching said extrusion.
 19. An improved heatexchanger tube according to claim 18 wherein said aluminum alloy furthercontains one or more of the following elements: up to about 0.8%magnesium, about 0.01-0.30% chromium, about 0.01-0.30% zirconium, about0.01-0.30% vanadium, about 0.01-0.30% cobalt, and about 0.01-2.0%nickel.
 20. An improved heat exchanger tube according to claim 18wherein said tube further comprises a coating of at least about 80 wt %zinc.
 21. A heat exchanger tube having enhanced corrosion resistance andimproved resistance to high burst pressures, said heat exchanger tubecomprising an aluminum alloy that consists essentially of about0.01-1.0% silicon, up to about 1.0% copper, up to about 1.8% manganese,about 0.05-0.8% iron, up to about 2.0% zinc, about 0.02-0.30% titaniumand the balance substantially aluminum and incidental elements andimpurities, wherein said aluminum alloy is continuously cast tofabricate a feedstock, said feedstock being a strip, rod, or sheet andhaving an aspect ratio ranging from about 1:1 to 500:1, said feedstockmay be exposed to elevated temperatures greater than about 300° C., saidfeedstock having an average secondary dendrite arm spacing less thanabout 100 microns and having a cross sectional area of about 2500 mm² orless and having a yield strength ranging from about 50 to about 150 MPa,and wherein said feedstock is extruded using a continuous rotaryextrusion process into an extrusion, and quenching said extrusion. 22.An improved heat exchanger tube according to claim 21 wherein saidaluminum alloy further contains one or more of the following elements:up to about 0.8% magnesium, about 0.01-0.30% chromium, about 0.01-0.30%zirconium, about 0.01-0.30% vanadium, about 0.01-0.30% cobalt, and about0.01-2.0% nickel.
 23. An improved heat exchanger tube according to claim21 wherein said tube further comprises a coating of at least about 80 wt% zinc.
 24. A heat exchanger tube having enhanced corrosion resistanceand improved resistance to high burst pressures, said heat exchangertube comprising an aluminum alloy that consists essentially of about0.01-0.50% silicon, up to about 0.7% copper, up to about 1.5% manganese,about 0.10-0.7% iron, up to about 1.5% zinc, up to about 0.02% titanium,and the balance substantially aluminum and incidental elements andimpurities, wherein said aluminum alloy is continuously cast tofabricate a feedstock, said feedstock being a strip, rod, or sheet andhaving an aspect ratio ranging from about 1:1 to about 500:1, saidfeedstock may be exposed to elevated temperatures greater than about300° C., said feedstock having an average secondary dendrite arm spacingless than about 100 microns and having a cross sectional area of about2500 mm² or less and having a yield strength ranging from about 50 toabout 150 MPa, and wherein said feedstock is extruded using a continuousrotary extrusion process into an extrusion, and quenching saidextrusion.
 25. An improved heat exchanger tube according to claim 24wherein said aluminum alloy further contains one or more of thefollowing elements: up to about 0.8% magnesium, about 0.01-0.28%chromium, about 0.01-0.28% zirconium, about 0.01-0.28% vanadium, about0.01-0.28% cobalt, and about 0.01-1.8% nickel.
 26. An improved heatexchanger tube according to claim 24 wherein said tube further comprisesa coating of at least about 80 wt % zinc.
 27. A heat exchanger tubehaving enhanced corrosion resistance and improved resistance to highburst pressures, said heat exchanger tube comprising an aluminum alloythat consists essentially of about 0.01-0.50% silicon, up to about 0.7%copper, up to about 1.5% manganese, about 0.10-0.7% iron, up to about1.5% zinc, about 0.02-0.25% titanium, and the balance substantiallyaluminum and incidental elements and impurities, wherein said aluminumalloy is continuously cast to fabricate a feedstock, said feedstockbeing a strip, rod, or sheet and having an aspect ratio ranging fromabout 1:1 to about 500:1, said feedstock may be exposed to elevatedtemperatures greater than about 300° C., said feedstock having anaverage secondary dendrite arm spacing less than about 100 microns andhaving a cross sectional area of about 2500 mm² or less and having ayield strength ranging from about 50 to about 150 MPa, and wherein saidfeedstock is extruded using a continuous rotary extrusion process intoan extrusion, and quenching said extrusion.
 28. An improved heatexchanger tube according to claim 27 wherein said aluminum alloy furthercontains one or more of the following elements: up to about 0.8%magnesium, about 0.01-0.28% chromium, about 0.01-0.28% zirconium, about0.01-0.28% vanadium, about 0.01-0.28% cobalt, and about 0.01-1.8%nickel.
 29. An improved heat exchanger tube according to claim 27wherein said tube further comprises a coating of at least about 80 wt %zinc.
 30. A multi layered extruded tube having improved resistance tohigh burst pressures, said multi layered tube having an inner core tubecomprising an aluminum alloy consisting essentially of about 0.01-1.5%silicon, up to about 1.2% copper, up to about 2.0% manganese, about0.01-1.0% iron, up to about 5.0% zinc, up to about 0.02% titanium, andthe balance substantially aluminum and incidental elements andimpurities, and one or more clad layers comprising an aluminum alloyselected from the group consisting essentially of the 1XXX, 2XXX, 3XXX,4XXX, 5XXX, 6XXX, 7XXX, and 8XXX series of aluminum alloys cladded on anexterior surface of said inner core, wherein said aluminum alloy is afeedstock, said feedstock being a strip, rod, or sheet and having anaspect ratio ranging from about 1:1 to about 500:1, said feedstock maybe exposed to elevated temperatures greater than about 300° C., saidfeedstock having an average secondary dendrite arm spacing less thanabout 100 microns and having a cross sectional area of about 2500 mm² orless and having a yield strength ranging from about 50 to about 150 MPa,and wherein said feedstock is extruded using a continuous rotaryextrusion process into an extrusion.
 31. A multi layered extruded tubeaccording to claim 30 wherein said extrusion is quenched or air cooledafter extrusion.
 32. A multi layered extruded tube according to claim 30wherein said aluminum alloy is continuously cast to fabricate saidfeedstock.
 33. A multi layered extruded according to claim 30 wherein anexterior surface of said extrusion is cladded with one or more cladlayers by using one or more tangential continuous rotary extrusionmachines.
 34. A multi layered extruded tube according to claim 30wherein said inner core tube further contains one or more of thefollowing elements: about 0.01-0.35% chromium, about 0.01-0.35%zirconium, about 0.01-0.35% vanadium, about 0.01-0.35% cobalt, up toabout 1.0% magnesium and about 0.01-2.5% nickel.
 35. A multi layeredextruded tube according to claim 30 wherein said clad layers are drawnor sinked over said inner core tube after cladding.
 36. A multi layeredextruded tube according to claim 30 wherein said tube further comprisesa coating of at least about 80 wt % zinc.
 37. A multi layered extrudedtube according to claim 30 wherein said clad layer is selected from thegroup consisting essentially of aluminum alloys 4343, 4045, and 4047,said clad layer having a thickness ranging from about 3 μm to about 300μm.
 38. A multi layered extruded tube according to claim 30 wherein oneclad layer has an electrochemical potential difference of at least about20 mV to about 40 mV when compared to said inner core tube or anadjacent clad layer.
 39. A multi layered extruded tube according toclaim 30 wherein said tube is a heat exchanger tube.
 40. A multi layeredextruded tube having enhanced corrosion resistance and improvedresistance to high burst pressures, said multi layered tube having aninner core tube comprising an aluminum alloy consisting essentially ofabout 0.01-1.5% silicon, up to about 1.2% copper, up to about 2.0%manganese, about 0.01-1.0% iron, up to about 0.01-5.0% zinc, about0.02-0.35% titanium and the balance substantially aluminum andincidental elements and impurities, and one or more clad layerscomprising an aluminum alloy selected from the group consistingessentially of the 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, 7XXX, and 8XXXseries of aluminum alloys cladded on an exterior surface of said innercore, wherein said aluminum alloy is continuously cast to fabricate afeedstock, said feedstock being a strip, rod, or sheet and having anaspect ratio ranging from about 1:1 to about 500:1, said feedstock maybe exposed to elevated temperatures greater than about 300° C., saidfeedstock having an average secondary dendrite arm spacing less thanabout 100 microns and having a cross sectional area of about 2500 mm² orless and having a yield strength ranging from about 50 to about 150 MPa,and wherein said feedstock is extruded using a continuous rotaryextrusion process into an extrusion, quenching said extrusion and usingone or more tangential continuous rotary extrusion machines to clad oneor more clad layers onto said exterior surface of said inner core tube.41. A multi layered extruded tube according to claim 40 wherein saidinner core tube further contains one or more of the following elements:about 0.01-0.35% chromium, about 0.01-0.35% zirconium, about 0.01-0.35%vanadium, about 0.01-0.35% cobalt, up to about 1.0% magnesium and about0.01-2.5% nickel.
 42. A multi layered extruded tube according to claim40 wherein said clad layers are drawn or sinked over said inner coretube after cladding.
 43. A multi layered extruded tube according toclaim 40 wherein said tube is a heat exchanger tube.
 44. A multi layeredextruded tube according to claim 40 wherein said tube further comprisesa coating of at least about 80 wt % zinc.
 45. A multi layered extrudedtube having enhanced corrosion resistance and improved resistance tohigh burst pressures, said multi layered tube having an inner core tubecomprising an aluminum alloy consisting essentially of about 0.01-1.0%silicon, up to about 1.0% copper, up to about 1.8% manganese, about0.05-0.8% iron, up to about 0.01-2.0% zinc, up to about 0.02% titaniumand the balance substantially aluminum and incidental elements andimpurities, and one or more clad layers comprising an aluminum alloyselected from the group consisting essentially of the 1XXX, 2XXX, 3XXX,4XXX, 5XXX, 6XXX, 7XXX, and 8XXX series of aluminum alloys cladded on anexterior surface of said inner core, wherein said aluminum alloy iscontinuously cast to fabricate a feedstock, said feedstock being astrip, rod, or sheet and having an aspect ratio ranging from about 1:1to about 500:1, said feedstock may be exposed to elevated temperaturesgreater than about 300° C., said feedstock having an average secondarydendrite arm spacing less than about 100 microns and having a crosssectional area of about 2500 mm² or less and having a yield strengthranging from about 50 to about 150 MPa, and wherein said feedstock isextruded using a continuous rotary extrusion process into an extrusion,quenching said extrusion and using one or more tangential continuousrotary extrusion machines to clad one or more clad layers onto saidexterior surface of said inner core tube.
 46. A multi layered extrudedtube according to claim 45 wherein said inner core tube further containsone or more of the following elements: up to about 0.8% magnesium, about0.01-0.30% chromium, about 0.01-0.30% zirconium, about 0.01-0.30%vanadium, about 0.01-0.30% cobalt, and about 0.01-2.0% nickel.
 47. Amulti layered extruded tube according to claim 45 wherein said cladlayers are drawn or sinked over said inner core tube after cladding. 48.A multi layered extruded tube according to claim 45 wherein said tube isa heat exchanger tube.
 49. A multi layered extruded tube according toclaim 45 wherein said tube further comprises a coating of at least about80 wt % zinc.
 50. A multi layered extruded tube having enhancedcorrosion resistance and improved resistance to high burst pressures,said multi layered tube having an inner core tube comprising an aluminumalloy consisting essentially of about 0.01-1.0% silicon, up to about1.0% copper, up to about 1.8% manganese, about 0.05-0.8% iron, up toabout 2.0% zinc, about 0.02-0.30% titanium and the balance substantiallyaluminum and incidental elements and impurities, and one or more cladlayers comprising an aluminum alloy selected from the group consistingessentially of the 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, 7XXX, and 8XXXseries of aluminum alloys cladded on an exterior surface of said innercore, wherein said aluminum alloy is continuously cast to fabricate afeedstock, said feedstock being a strip, rod, or sheet and having anaspect ratio ranging from about 1:1 to about 500:1, said feedstock maybe exposed to elevated temperatures greater than about 300° C., saidfeedstock having an average secondary dendrite arm spacing less thanabout 100 microns and having a cross sectional area of about 2500 mm² orless and having a yield strength ranging from about 50 to about 150 MPa,and wherein said feedstock is extruded using a continuous rotaryextrusion process into an extrusion, quenching said extrusion and usingone or more tangential continuous rotary extrusion machines to clad oneor more clad layers onto said exterior surface of said inner core tube.51. A multi layered extruded tube according to claim 50 wherein saidinner core tube further contains one or more of the following elements:up to about 0.8% magnesium, about 0.01-0.30% chromium, about 0.01-0.30%zirconium, about 0.01-0.30% vanadium, about 0.01-0.30% cobalt, and about0.01-2.0% nickel.
 52. A multi layered extruded tube according to claim50 wherein said clad layers are drawn or sinked over said inner coretube after cladding.
 53. A multi layered extruded tube according toclaim 50 wherein said tube is a heat exchanger tube.
 54. A multi layeredextruded tube according to claim 50 wherein said tube further comprisesa coating of at least about 80 wt % zinc.
 55. A multi layered extrudedtube having enhanced corrosion resistance and improved resistance tohigh burst pressures, said multi layered tube having an inner core tubecomprising an aluminum alloy consisting essentially of about 0.01-0.50%silicon, up to about 0.7% copper, up to about 1.5% manganese; about0.10-0.7% iron, up to about 1.5% zinc, up to about 0.02% titanium, andthe balance substantially aluminum and incidental elements andimpurities, and one or more clad layers comprising an aluminum alloyselected from the group consisting essentially of the 1XXX, 2XXX, 3XXX,4XXX, 5XXX, 6XXX, 7XXX, and 8XXX series of aluminum alloys cladded on anexterior surface of said inner core, wherein said aluminum alloy iscontinuously cast to fabricate a feedstock, said feedstock being astrip, rod, or sheet and having an aspect ratio ranging from about 1:1to about 500:1, said feedstock may be exposed to elevated temperaturesgreater than 300° C., said feedstock having an average secondarydendrite arm spacing less than about 100 microns and having a crosssectional area of about 2500 mm² or less and having a yield strengthranging from about 50 to about 150 MPa, and wherein said feedstock isextruded using a continuous rotary extrusion process into an extrusion,quenching said extrusion and using one or more tangential continuousrotary extrusion machines to clad one or more clad layers onto saidexterior surface of said inner core tube.
 56. A multi layered extrudedtube according to claim 55 wherein said inner core tube further containsone or more of the following elements: up to about 0.8% magnesium, about0.01-0.28% chromium, about 0.01-0.28% zirconium, about 0.01-0.28%vanadium, about 0.01-0.28% cobalt, and about 0.01-1.8% nickel.
 57. Amulti layered extruded tube according to claim 55 wherein said cladlayers are drawn or sinked over said inner core tube after cladding. 58.A multi layered extruded tube according to claim 55 wherein said tube isa heat exchanger tube.
 59. A multi layered extruded tube according toclaim 55 wherein said tube further comprises a coating of at least about80 wt % zinc.
 60. A multi layered extruded tube having enhancedcorrosion resistance and improved resistance to high burst pressures,said multi layered tube having an inner core tube comprising an aluminumalloy consisting essentially of about 0.01-0.50% silicon, up to about0.7% copper, up to about 1.5% manganese; about 0.10-0.7% iron, up toabout 1.5% zinc, about 0.02-0.25% titanium and the balance substantiallyaluminum and incidental elements and impurities, and one or more cladlayers comprising an aluminum alloy selected from the group consistingessentially of the 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, 7XXX, and 8XXXseries of aluminum alloys cladded on an exterior surface of said innercore, wherein said aluminum alloy is continuously cast to fabricate afeedstock, said feedstock being a strip, rod, or sheet and having anaspect ratio ranging from about 1:1 to about 500:1, said feedstock maybe exposed to elevated temperatures greater than about 300° C., saidfeedstock having an average secondary dendrite arm spacing less thanabout 100 microns and having a cross sectional area of about 2500 mm² orless and having a yield strength ranging from about 50 to about 150 MPa,and wherein said feedstock is extruded using a continuous rotaryextrusion process into an extrusion, quenching said extrusion, and usingone or more tangential continuous rotary extrusion machines to clad oneor more clad layers onto said exterior surface of said inner core tube.61. A multi layered extruded tube according to claim 60 wherein saidinner core tube further contains one or more of the following elements:up to about 0.8% magnesium, about 0.01-0.28% chromium, about 0.01-0.28%zirconium, about 0.01-0.28% vanadium, about 0.01-0.28% cobalt, and about0.01-1.8% nickel.
 62. A multi layered extruded tube according to claim60 wherein said clad layers are drawn or sinked over said inner coretube after cladding to help consolidate various layers.
 63. A multilayered extruded tube according to claim 60 wherein said tube is a heatexchanger tube.
 64. A multi layered extruded tube according to claim 60wherein said tube further comprises a coating of at least about 80 wt %zinc.
 65. A method of making an improved heat exchanger tube comprising:continuously casting a feed stock; and extruding said feed stock througha continuous extrusion rotary process to form said heat exchanger tube.66. A method of making an improved heat exchanger tube according toclaim 65 wherein quenching or air cooling said heat exchanger tube aftersaid continuous extrusion rotary process.